Two minimally invasive assays for detecting prions that are diagnostic of Creutzfeldt–Jakob disease (CJD) in living patients show promise, according to preliminary studies published August 7 in the New England Journal of Medicine.
One assay tests epithelial samples obtained from nasal brushings, and the other tests urine samples. Both tests can be used in patients suspected of having the sporadic, inherited, or acquired forms of CJD, such as variant CJD and iatrogenic CJD. Both assays had sensitivities and specificities ranging between 93% and 100% in small patient populations in these exploratory studies. This range of sensitivities and specificities is better than the diagnostic accuracy of CSF testing.
If these findings are replicated in larger studies, both assays will have the potential for establishing a definitive diagnosis of CJD in clinical settings. The test that uses nasal brushings may establish a definitive diagnosis earlier in the course of the disease than has been possible previously, thus potentially enabling intervention for this fatal neurodegenerative disorder.
In addition, the incidental finding that simple brushing of the olfactory mucosa yields a greater quantity of prion seeds than is found in CSF suggests that infectivity may be present in the nasal cavity, which has important biosafety implications, the researchers noted.
Epithelial Test Had 100% Specificity
In the first report, investigators applied real-time quaking-induced conversion technology to olfactory epithelium samples from 31 patients who had rapidly progressive dementia and were referred for evaluation of possible or probable CJD. These patients concurrently underwent CSF sampling. Twelve patients with other neurodegenerative disorders, primarily Alzheimer’s disease or Parkinson’s disease, and 31 patients who had no neurologic disorders were controls, said Christina D. Orrú, PhD, a researcher at the Laboratory of Persistent Viral Diseases at the National Institute of Allergy and Infectious Diseases’s Rocky Mountain Laboratories in Hamilton, Montana, and her colleagues.
Obtaining the nasal brushings was described as a gentle procedure in which unsedated patients were first given a local vasoconstrictor applied with a nasal tampon, and then had a fiber-optic rhinoscope with a disposable sheath inserted into the nasal cavity to locate the olfactory mucosal lining of the nasal vault. A sterile, disposable brush was inserted alongside the rhinoscope, gently rolled on the mucosal surface, withdrawn, and immersed in saline solution in a centrifuge tube for further preparation.
The assays using this material yielded positive results for all 15 patients who had definite sporadic CJD, 13 of the 14 who had probable sporadic CJD, and both patients who had inherited CJD. In contrast, all 43 controls had negative results. This performance represents a sensitivity of 97% and a specificity of 100% in this study population. In comparison, testing of CSF samples from the same patients had a 77% sensitivity, said Dr. Orrú and her associates.
The substantial prion seeding in the olfactory mucosa, which was of greater magnitude than that in the CSF, raises the possibility that CJD prions could contaminate patients’ nasal discharges. “Nasal and aerosol-borne transmission of prion diseases have been documented in animal models, but there is no epidemiologic evidence for aerosol-borne transmission of sporadic CJD” to date, the investigators wrote.
Medical instruments that come into contact with the nasal mucosa may become contaminated with prions, “which poses the question of whether iatrogenic transmission is possible. Therefore, further study of possible biohazards ... is warranted,” the authors concluded.
Urine Test Was Highly Sensitive
In the second study, Fabio Moda, PhD, then a postdoctoral fellow at the Mitchell Center for Research in Alzheimer’s Disease and Related Brain Disorders at the University of Texas in Houston, and his associates assayed urine samples for minute quantities of the misfolded prion protein using an extensive amplification technology. The group tested samples from 68 patients with sporadic CJD, 14 with variant CJD, and 156 controls. The control group included four patients with genetic prion diseases, 50 with other neurodegenerative disorders (eg, Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, motor neuron disease, and progressive supranuclear palsy), 50 patients with nondegenerative neurologic disorders (chiefly cerebrovascular disease, multiple sclerosis, epilepsy, brain tumors, autoimmune encephalitis, and meningitis), and 52 healthy adults.
This assay had a sensitivity of 93% and a specificity of 100% in distinguishing CJD from other brain disorders and from brain health in this patient population, said the authors. The quantities of the prion protein excreted in the urine were extremely small, so the researchers did not address the potential for infectivity in this study.
Better Specificity Estimates Are Needed
These findings are encouraging because clinicians and researchers have long sought a sensitive and minimally invasive diagnostic tool specifically targeted to the protein that causes all forms of CJD, said Colin L. Masters, MD, Deputy Director of Mental Health at the Florey Institute of Neuroscience and Mental Health, University of Melbourne, in an accompanying editorial.